I have no idea I need the answer too
The answers is an electrical force.
Under normal conditions, atoms interact with each other via electrons that are furthest away from the nucleus. These electrons from the what is called the outer shell of the atom, electrons from the outer shell that can participate in chemical reactions are called valence electrons.
To solve this problem we need to apply the corresponding sound intensity measured from the logarithmic scale. Since in the range of intensities that the human ear can detect without pain there are large differences in the number of figures used on a linear scale, it is usual to use a logarithmic scale. The unit most used in the logarithmic scale is the decibel yes described as

Where,
I = Acoustic intensity in linear scale
= Hearing threshold
The value in decibels is 17dB, then

Using properties of logarithms we have,




Therefore the factor that the intensity of the sound was 
Answer
given,
angle between two polarizing filters = 45°
filter reduce intensity = ?
a) I = I₀ Cos² θ
here θ = 45⁰
intensity of the light is reduced by 0.500
correct answer from the given option D
b) direction of the polarization
θ = 45°